Arc-back indicator



Oct. 8, 1940.

WITNESSES:

L. R. LUDWIG ARC-BACK INDICATOR Filed March 51, 1938 INVENTOR Zea/7 Eduo W1? ATTORNEY Patented Oct. 8, 1940 PATENT OFFICE ABC-BACK INDICATORLeon B. Ludwig, Wilkinsburg, Pat, alsignor to Westinghouse Electric &.Manufacturing Company, East Pittsburgh, Pa., a corporation PennsylvaniaApplication March :1, 1938, Serial No. 199,215

2 Claims. (Cl. 177-311) My invention relates to a fault-responsivedevice and more particularly to a relay responsive to inverse currentsin a vapor-electric converter.

In the operation of vapor-electric converters 6 of the type used fortransferring energy between alternating-current and direct-currentsystems, there is the disadvantage in that such converters are subjectto temporary reverse currents known in the art as arc-backs. Means andmethods for l disconnecting the converter or detecting arcbacks is notunknown in the art. Prior art devices, of which I am aware, are of theinductive type: that is, their operation is dependent upon the rate ofrise of current. Moreover, previous arc-back responsive devices have aninherent disadvantage in that they respond to load conditions andtransients in the circuit which might give false indications.

According to my invention, I have found it preferable to rely on anarc-back responsive device which may be called one of the electronictype in that such a device is free of transients and is more likely togive a faithful indication of operating conditions in the converter.

Briefly, I use an oscillographic element which is operatively connectedin parallel with a millivolt shunt placed in the direct-current circuitof the converter through which current normally i'iows in one direction.A beam of light is dinoted upon a mirror forming part of theoscillographic element which is normally reflected in a direction awayfrom some light-sensitive device, such as a photo-electric cell.However. upon the occurrence of a reverse current in the direct-currentcircuit, the oscillographic element turns the mirror so that a lightbeam is thrown upon the photo-electric cell, .which in turn transformsthe light received intoelectrical impulses. A suitable valve. such as agrid-controlled discharge device, breaks down and consequently operatesa suitable relay device.

It is, therefore, an object of my invention to provide an arc-backresponsive device which is itself free from transients that might givefalse indications.

Another object of my invention is to provide an automatically operatedarc-back responsive device which is reliable andnoiseless in operation.

It is a further object of my invention to pro-.

vide an arc-back responsive device which can be operated only when areverse current flows in a unidirectional conductor 'attachedeto thevaporelectric converter.

Other objects and advantages of my invention will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawing, in which the single figure is a diagrammaticillustration oi an arc-back responsive device embodying my invention.

The apparatus according to my invention com- 5 prises a currentrectifying device 3, such as a mercury arc converter, having a circuit5, supplying direct current to a load 1. The converter 3 comprises ananode 3, a mercury pool cathode l l, and a make-alive electrode II forestablishing the 10 cathode spots. The make-alive electrode I3 isconnected to the anode I through a suitable uni directional conductorl5, such as a half wave rec tifler. In series with the anode 8 is placeda millivolt shunt II which normally carries current 5 in one direction.In parallel with the shunt I1 is attached a suitable magneticallyoperated light reflector H, such as an oscillograph, including a lightreflecting element It, such as arnirror. A source of light from anincandescent lamp 23 pro- 20 vides a beam of light which is focused bythe lens 25 to produce a narrow beam on the mirror ll of theoscillograph I 3. A suitable shield 2'! prevents light from spreading inall but the desired direction. 25

A light-responsive device 23, such as a photoelectric cell, is suitablyplaced in the vicinity of the oscillograph II to pick up light that maybe reflected from the reflecting element 2| when the latter is movedinto a certain position. A suitable 30 control device 3|, such as agrid-controlled discharge device, is connected in series with thephoto-electric cell 28. The auxiliary discharge device 3| has a' voltagecharacteristic such that under normal operating conditions the grid 33 5of the discharge device 3| is sufllciently negative to prevent abreakdown. Associated with the auxiliary discharge device 3| is anactuating coil 35 of a circuit breaker or annunciator or any suchsimilar device may be attached. N 40 In the operation of my device 3,current normally flows in the shunt I I in one direction so that theoscillograph I! will cause the mirror 2| to deflect the projected lightbeam in a direction away from the photo-electric cell 29. However, 45 ifa reverse current flows in the shunt ll, the oscillograph I! will swingthe light reflecting element 2| through an angle, thereby reflecting theincident light from the source 23 towards the photo-electric cell 29,thus energizing it. Simul- 50 taneously, with the pickup of thereflected light, the photo-electric cell 29 produces an electricalimpulse which is impressed on the grid 33 of the auxiliary dischargedevice 3|, permitting the same .to break down, and thus actuating a coil35 of a relay, or possibly an actuating coil of a circuit breaker.

While I have shown and described certain speciflc embodiments of myinvention, it is apparent that changes and modifications can be madetherein without departing from the true spirit of my invention or thescope of the appended claims.

I claim as my invention:

l. An inverse current responsive relay comprising a conductor normallycarrying current in only one direction, a shunt in said conductor, anoscillograph element connected in parallel to said shunt, a lightreflecting element actuated by said oscillograph element, a light sourcecooperating with said light reflecting element, said light reflectingelement reflecting light in one direction during normal direction ofcurrent flow through said shunt and in another direction during abnormaldirection of current flow therein, a light responsive means energized bythe light amuse during inverse current flow in said shunt and circuitmeans operatively connected to said light responsive means.

2. An arc-back responsive relay for a vapor electric device comprising aconductor connected to said device, said conductor carrying current inone direction during normal operation of the device and in an inversedirection during an areback, a shunt in said conductor, an oscillographelement connected in parallel with said shunt, said oscillograph elementbeing movable in one direction in response to normal current directionin said shunt and in the opposite direction in response to inversecurrent, a light reflecting element carried by said oscillographelement, a light source tor said light reflecting element, aphoto-electric device positioned to be energized by the light from saidlight reflecting element during the occurrence of inverse current insaid shunt.

LEON R. LUDWIG.

